In this paper protocols for group key distribution are compared and evaluated from the point of view of Mobile Ad Hoc Networks (MANETs). A MANET is a collection of wireless mobile nodes, communicating among themselves over possibly multihop paths, without the help of any infrastructure such as base stations or access points. So the need to render those networks as autonomous and secure as possible, since no central authorization can be assumed at all times, becomes emergent. Key management is the service that ensures the security of communication among nodes, and the capability of their cooperation as a secure group. It consists of three important services: key generation, user authentication and key distribution. In this work we assume that the participating users have already been authenticated with some mechanism, and we are focused only on studying and comparing protocols for group key establishment in MANETs. We distinguish the protocols in two families, the contributory and non-contributory and we evaluate them from the point of view of MANETs.